mremap - re-map a virtual memory address
void * mremap(void *old_address, size_t old_size
, size_t new_size, unsigned long flags);
expands (or shrinks) an existing memory mapping, potentially
moving it at the same time (controlled by the flags
the available virtual address space).
old_address is the old address of the virtual memory block that you
want to expand (or shrink). Note that old_address has to be page
aligned. old_size is the old size of the
virtual memory block. new_size is the requested size of the
virtual memory block after the resize.
The flags argument is a bitmap of flags.
In Linux the memory is divided into pages. A user process has (one or)
several linear virtual memory segments. Each virtual memory segment has one
or more mappings to real memory pages (in the page table). Each virtual
memory segment has its own protection (access rights), which may cause
a segmentation violation if the memory is accessed incorrectly (e.g.,
writing to a read-only segment). Accessing virtual memory outside of the
segments will also cause a segmentation violation.
mremap uses the Linux page table scheme. mremap changes the
mapping between virtual addresses and memory pages. This can be used to
implement a very efficient realloc.
indicates if the operation should fail, or change the virtual address
if the resize cannot be done at the current virtual address.
On success mremap
returns a pointer to the new virtual memory area.
On error, the value
(that is, (void *) -1) is returned, and errno
is set appropriately.
An invalid argument was given. Most likely old_address was not
"Segmentation fault." Some address in the range
old_address to old_address+old_size is an invalid
virtual memory address for this process.
You can also get EFAULT even if there exist mappings that cover the
whole address space requested, but those mappings are of different types.
The memory segment is locked and cannot be re-mapped.
The memory area cannot be expanded at the current virtual address, and the
flag is not set in flags.
Or, there is not enough (virtual) memory available.
With current glibc includes, in order to get the definition of
you need to define _GNU_SOURCE before including <sys/mman.h
This call is Linux-specific, and should not be used in programs
intended to be portable. 4.2BSD had a (never actually implemented)
call with completely different semantics.
Your favorite OS text book for more information on paged memory.
(Modern Operating Systems
by Andrew S. Tannenbaum,
by Randolf Bentson,
The Design of the UNIX Operating System
by Maurice J. Bach.)
- RETURN VALUE
- CONFORMING TO
- SEE ALSO